JPS63194330A - Method for exposing semiconductor - Google Patents

Abstract

PURPOSE:To realize an alignment accuracy of about 0.2 mum or less and to improve the yield of producing LSI's having a line width of submicron order, by applying P-polarized light to a wafer on which resist is applied, the P- polarized light being incident at a Brewster angle with respect to the resist surface. CONSTITUTION:A target mark 21 is formed on a wafer 2 in repeated pattern having a width of 6 mum and a pitch of 1.4 mum, for example. P-polarized light which is incident at a Brewster angle with respect to the pattern is applied against the target. For the purpose of obtaining high directivity, laser beams are used. Since all the P-polarized light incident at a Brewster angle is transmit ted, no light is reflected from the resist surface while reflected light represents uneven configurations of the wafer target pattern. If the resist surface is uneven, the reflected light from the target mark performs change in phase corresponding to variances in thickness of the resist but it does not present an extremely asymmetrical waveform. Thus, the pattern position can be detected with high precision.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a semiconductor exposure method for aligning a mask and a wafer to accurately overlay and expose a circuit pattern on the mask onto the wafer. A semiconductor exposure method suitable for dealing with uneven coating of a resist coated on top was discovered.

[Conventional technology]

As a conventional semiconductor exposure method, Japanese Patent Application Laid-Open No. 60-9862
Publication No. 5 is known.

[Problem that the invention seeks to solve]

Printing of semiconductor circuit patterns is mainly performed using a reduction exposure device, but in order to expose a wide exposure area with high resolution and low distortion, the reduction lens resolves only light with a narrow spectral width. Therefore, chromatic aberration occurs for broadband spectral light, and the resolution is extremely reduced. For this reason,
The light used for alignment for aligning the mask and wafer must also have a narrow spectrum. However, when a wafer pattern is detected under a narrow spectrum, multiple interference occurs between the alignment target mark of the evaporator and the surface of the resist coated on +(7). On the other hand, in recent years, in order to improve semiconductor production yields, increasingly larger diameter wafers have been used.As the diameter of the wafer increases, it becomes increasingly difficult to apply resist uniformly to the wafer. In particular, the resist thickness is not symmetrical with respect to the step part of the target mark, and due to multiple interference,
Asymmetry occurs in the Turkerato mark detection signal, resulting in a decrease in alignment accuracy. Figure 2 is a diagram explaining this phenomenon, and shows that the resist film thickness at point ABC of target mark 21 is to, d+, do+Δd, and point A and 0.
If there is a difference in film thickness due to uneven coating at points, see Figure 2 C.
As shown in b), the detected waveform becomes asymmetric between point A and point 0. As a result, the center of the pattern cannot be detected, resulting in a decrease in alignment accuracy.

As described above, in the above-mentioned conventional technology, since the resist film thickness becomes asymmetric on both sides of the pattern due to one coating unevenness, a problem arises because the interference intensity changes rapidly with a small film thickness due to multiple interference.

The purpose of the present invention is to avoid changes in interference intensity due to slight changes in coating unevenness, to perform detection that is less susceptible to coating unevenness, and to align the mask and wafer to detect circuit patterns on the mask. An object of the present invention is to provide a semiconductor exposure method for exposing a wafer.

[Means for solving problems]

The above object is to make the light that illuminates a wafer coated with resist enter the resist surface at Brewster's angle, and to make the incident light incident as P-polarized light, thereby producing reflected light that is directly reflected on the resist surface.

This is achieved by leveling the wafer and extracting only the light reflected by the pattern on the wafer.

[Effect]

As shown in FIG. 3, P-polarized light 501 incident on the wafer at Brewster's angle becomes light 5 directly reflected on the resist surface.
02' becomes almost 0 level. Figure 3<b> shows how the relative amplitude of reflected light changes depending on the incident angle and polarization state.
The Priest angle is approximately 600 degrees. Since there is no reflection on the resist surface, all reflected light components are reflected on the surface of the target mark, and the influence of coating unevenness is significantly reduced.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In the 11th A, 1 is a mask (reticle) that is the original image of the circuit pattern. The pattern of the mask is imaged onto the wafer 2 by a reducing lens 3. Reference numeral 4 denotes an exposure light source, and the light emitted from this illuminates the mask, and the transmitted light forms an image on the wafer as a small pattern of the mask and exposes it. To make semiconductor integrated circuits, a number of different patterns are printed on wafers, developed, and etched, among other steps. In order to achieve this overlapping exposure with good compensation, it is necessary to accurately determine the relative position af between the alignment mark 11 on the mask 1 and the alignment mark (target mark) 21 on the wafer, and to drive the wafer to a predetermined position using the table 7. be. The target mark 21 on the wafer 2 has a pitch of 6 μm and a pitch of 14 μm, as shown in 1d(b).
m repeating pattern. For this pattern, the target is irradiated with P-polarized light having a Brewster angle as shown in the step view (side view) of the wafer in FIG. 1(C).

In order to irradiate such highly directional light, laser light is used as the illumination light. P incident at Briester angle
Since all polarized light is transmitted, reflected light that is faithful to the step shape of the wafer target pattern without reflection from the resist surface can be obtained. Naturally, if the resist surface is uneven, a phase change corresponding to this film thickness change will be carried on the target mark reflected light, but the conventional multiple reflection signal (Figure 2 (b)) It does not result in a large asymmetric waveform at the detection level 1J level such as . In other words, the phase change Δφ due to coating unevenness of Δd is 2π Δφ=7(ru 1) Δd, whereas the multiple interference intensity is ΔI=−6 Δφ which undergoes the intensity change Δ■ with respect to the phase change of Δφ In other words, on △φ and △φ, the ratio of phase change is approximately rL−1=2
When rL- and n=1.7, the ratio becomes 0.7:3.4, and the influence on the film thickness change is reduced to about /. In this way, a reflected light with a small shadow 9 can be obtained with respect to the change in the film 4, but since the Brewster angle θB is usually as large as 50° to 60°, the chick 31 of the 1-reducing lens 3 is Reflected light 502 is not incident. Therefore, the target mark is provided with a fine repeating pattern as shown in FIG. The detection light that has passed through the pupil 31 connects to the reticle 1 or its vicinity (if there is chromatic aberration), so this light is reflected by the 1-ticle 1 and detected. lead to 35,
Detect the wafer diffraction image.

The detected image is bright in some parts of the repeating pattern and dark in other parts. Moreover, even if there is a coating error in the vicinity of the pattern, a large asymmetrical change in the detection number 1g as shown in FIG. 2(b) does not occur due to this error, making it possible to detect the pattern position with high accuracy.

FIG. 4 shows another embodiment of the invention. The wafer target mark is a long bar-shaped mark shown in FIG. 4(h).

This mark is irradiated with P-polarized light at a breaster angle as shown in FIG. 4(b)(0), and the scattered light is detected. If the numbers attached to the parts in FIG. 4 match those of the parts in FIG. 1, they represent the same thing. Only one pattern detector is shown in both Figures 1 and 4. Figure 1 is for y-direction detection, and Figure 4 is for two-direction detection.
One is omitted in each figure. Fourth
In the example shown in the figure, the edge of the pattern is bright and the rest is dark, but in this case as well, there is no reflection on the resist surface.
High precision detection is achieved.

〔Effect of the invention〕

As explained above, according to the present invention, the reflection of the laser illumination light on the resist surface becomes zero, and the step information of the wafer target mark can be detected more accurately. As a result, the alignment accuracy, which conventionally was 0.25 μm or more due to resist coating unevenness, and in extreme cases was 0.4 μm or more, can now be adjusted to within 2 μm. As a result, L of submicron line 1
It has become possible to significantly increase the production yield of SI.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a principle diagram showing how a signal is output in a conventional detection method, and Fig. 5 is an explanation of reflected light showing the basic principle of detection of the present invention. Figure, 4th
The figure shows another embodiment of the present invention. 1...Mask, 2...Ueno), 21
... Wafer target mark 1 3 ... Reduction lens, 4 ... Illumination light source 15.
...Pattern detector. 11 no'

Claims (1)

[Claims] 1. P-polarized light is incident on the alignment mark on the wafer at Brewster's angle, and the reflected light from this alignment mark is imaged by an exposure lens as an image of the alignment mark. The image is captured by an imaging device and converted into a video signal. Based on the converted video signal, the position of the alignment mark is detected and aligned with the mask, and the circuit pattern formed on the mask is exposed onto the wafer. A semiconductor exposure method characterized by: 2. The semiconductor exposure method according to claim 1, wherein the alignment mark on the wafer is a mark having a periodic structure. 3. The semiconductor exposure method according to claim 2, wherein the light incident on the alignment mark on the wafer is made such that the direction of periodic change of the mark is parallel to the incident plane. .